Conventional fuel injectors typically employ two separate plungers or pistons which trap and compress two separate volumes of fuel. The first plunger is interconnected to the cam shaft and the second plunger is free floating within the fuel compression chamber. Fuel is delivered and removed from the fuel chamber by various networks of fuel lines having fuel ports positioned around the chamber walls. In addition, a control valve or switch is positioned along the fuel supply lines, between the chamber and the fuel reservoir, and controls the supply of fuel to the chamber. However, this type of injector has numerous inherent deficiencies.
First, because the fuel supply lines are routed directly to the fuel chamber, the control valve is exposed to the extreme changes in fuel pressure associated with the repeating injection cycle of engine operation. In particular, the control valve must operate under extreme conditions in which the fuel pressure may exceed 20,000 pounds per square inch during the compression phase. Consequently, in order to maintain the accuracy and efficiency of the overall system under these conditions, a bulky and costly control valve is required. This added cost increases the overall price of the engine and the necessary size of the valve requires it to be mounted apart from the injector thereby increasing the space requirements for the engine, increasing the length of the fuel lines running from the control switch to the fuel chamber and increasing the volume of fuel needed to fill the supply lines.
Second, conventional systems typically have numerous fuel ports spaced about the walls of the fuel chamber to allow fuel to enter and exit the chamber. This is especially true in dual plunger systems in order to accommodate the free floating plunger. However, the high fuel pressure created during the compression phase can cause the fuel chamber to expand or dialate which, in turn, causes fuel to leak from the various ports into the chamber. As a result, the fuel pressure will change, the fuel volume within the chamber will change, and consequently, the efficiency of the system, which depends upon consistent operating conditions, will decrease.
Third, conventional dual plunger injection systems, which utilize two separate trapped volumes of fuel, have a delayed response during fuel compression. The floating plunger acts like a resistive spring when converting the mechanical energy of the plunger into hydraulic energy and, as a result, it takes a longer period of time to reach injection pressure. Moreover, two separate volumes of fuel require more energy to compress in comparison to a single volume of lesser quantity. In addition, with the control switch mounted external to the injector as a result of its size, an additional volume of fuel is added to the total volume of fuel which must be compressed to the required level of injection pressure before the fuel can be injected into the engine cylinder. Consequently, conventional systems of this type require significant amounts of energy to operate and have long response times which as a result, make them less efficient.
A still further problem inherent in conventional fuel injectors is that they do not operate consistently between idle and high speeds. Because the injector is mechanically linked to the crankshaft, the plunger operates slower at idle and low engine speeds and faster at high engine speeds. As a result, the pressure created in the fuel chamber at low speeds may not be adequate to efficiently operate the engine. To remedy this, the profile of the operating cam can be changed so that the plunger moves fast enough at low speeds to create sufficient injector pressure. However, this typically creates too high of a pressure level at high engine speeds which can literally destroy the injectors. Consequently, a cam profile is typically chosen which balances the two extremes to create sufficient fuel injection pressure at all engine speeds. However, this type of balancing decreases the efficiency of the injector.